1. Field of Invention
This invention relates to the use of expansion anchors in bore holes formed in concrete anchorages or the like, as for example, concrete foundation walls, reinforced concrete column supports for elevated structures, and similar installations.
2. Prior Art
The relevant prior art consists of (a) expansion bolts, such as shown in applicant's U.S. Pat. No. 3,742,809 issued on July 3, 1973, and applicant's U.S. Pat. No. 3,848,506 issued Nov. 19, 1974, and (b) expansion studs such as shown in the following patents:
______________________________________ U.S. Pats. 2,896,494 Lerick July 28, 1959 3,107,569 Lerick October 22, 1963 3,257,891 Lerich June 28, 1966 3,277,770 McCulloch October 11, 1966 3,352,193 Lerich November 14, 1967 3,448,651 Passer June 10, 1969 3,546,998 Lerich December 15, 1970 3,703,119 Lerich November 21, 1972 3,750,526 Lerich August 7, 1973 Foreign Patents 899,669 Canadian May 9, 1972 ______________________________________
To the extent that applicant's own U.S. Pat. Nos. 3,742,809 and 3,848,506 provide an expansion sleeve which expands radially in perpendicular relation to the longitudinal axis of the bolt and the wall of the bore hole, these patents accomplish substantially the same result which is sought to be accomplished by the present invention. However, the means for achieving this result are different as between these issued patents and the present invention.
In the patents the tapered wedge tip of the bolt is threaded to receive an internally tapered and threaded expansion sleeve. In the present invention the tapered wedge tip of the stud is not threaded and it accomodates an internally tapered but non-threaded expansion sleeve. At their opposite end, the bolts of applicant's issued patents are headed, as bolts generally are, while the corresponding end of the stud of the present invention is threaded to receive a nut. The bolts of these patents must be rotated to expand the sleeves; in the present invention the nut is rotated for the same purpose, the stud remaining fixed in terms of angular movement.
In the second group of prior art patents, the expansion anchors are shown in the form of studs wherein neither the tapered wedge tip of the stud nor the interior tapered wall of the expansion anchor is threaded. To that extent these patents correspond to the invention of the present application.
Among these prior art patents are those wherein the expansion sleeve expands at an angle other than 90.degree. with respect to the longitudinal axis of the stud and the wall of the bore hole. Illustrative is Passer U.S. Pat. No. 3,448,651 wherein FIG. 5 of the drawing graphically shows an angular expansion of the extension sleeve. The upper end of the expansion sleeve is wedged against the bore hole wall under less pressure than the lower end and this pressure disparity reduces the effective grip contact area of the expansion sleeve.
Other prior art patents appear to provide expansion elements which do expand in perpendicular relation to the longitudinal axis of the stud and to the wall of the bore hole. Illustrative is Lerick U.S. Pat. No. 2,896,494. However, the expansion element of Lerick are small, e.g., 90.degree., segments of a circumferencial sleeve and neither their wedging surfaces nor the wedging surfaces of the stud are conically tapered.
Other prior art patents have different features or deficiencies which distinguish them from the present invention. For example, Lerich U.S. Pat. No. 3,352,193 has an expansion sleeve whose length corresponds, substantially, to the length of the wedge tip. Consequently, when the stud is displaced, to any appreciable extent, relative to the expansion sleeve, in order to cause expansion thereof, the lower end of the sleeve will project beyond the lower end of the wedge tip and will be unsupported thereby. The unsupported part of the expansion sleeve cannot exert a strong wedging action against the wall of the bore hole.
Lerich U.S. Pat. No. 3,546,998 shows an expansion sleeve which appears to be conically tapered both externally and internally. Even if expansion of this sleeve were considered to be perpendicular to the longitudinal axis of the stud and the wall of the bore hole, the non-cylindrical outer configuration of the sleeve would preclude uniform pressure on the bore hole wall. The larger end of the external taper would apply greater pressure and at an earlier phase of the wedging operation than the smaller end. Further, the larger end of the tapered expansion sleeve, when in unexpanded state, has a substantially larger diameter than the shank of the stud, and this would require a considerably larger bore hole than would be the case with an expansion sleeve whose diameter, prior to expansion, corresponds to the diameter of the stud shank.